Nicholas G. Heavens

Correction to “Extensive MRO CRISM observations of 1.27 µm O2 airglow in Mars polar night and their comparison to MRO MCS temperature profiles and LMD GCM simulations”

The Martian polar night distribution of 1.27 μm (0-0) band emission from O 2 singlet delta [O 2 ( 1 Δ g )] is determined from an extensive set of Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectral Mapping (CRISM) limb scans observed over a wide range of Mars seasons, high latitudes, local times, and longitudes between 2009 and 2011. This polar nightglow reflects meridional transport and winter polar descent of atomic oxygen produced from CO 2 photodissociation. A distinct peak in 1.27 μm nightglow appears prominently over 70-90NS latitudes at 40-60 km altitudes, as retrieved for over 100 vertical profiles of O 2 ( 1 Δ g ) 1.27 μm volume emission rates (VER). We also present the first detection of much (x80±20) weaker 1.58 μm (0-1) band emission from Mars O 2 ( 1 Δ g ). Co-located polar night CRISM O 2 ( 1 Δ g ) and Mars Climate Sounder (MCS, McCleese et al, 2007) temperature profiles are compared to the same profiles as simulated by the Laboratoire de Meteorologie Dynamique (LMD) general circulation/photochemical model (e.g., Lefevre et al, 2004). Both standard and interactive aerosol LMD simulations (Madeleine et al, 2011) underproduce CRISM O 2 ( 1 Δ g ) total emission rates by 40%, due to inadequate transport of atomic oxygen to the winter polar emission regions. Incorporation of interactive cloud radiative forcing on the global circulation leads to distinct but insufficient improvements in modeled polar O 2 ( 1 Δ g ) and temperatures. The observed and modeled anti-correlations between temperatures and 1.27 μm band VER reflect the temperature dependence of the rate coefficient for O 2 ( 1 Δ g ) formation, as provided in Roble (1995).

Seasonal and diurnal variability of detached dust layers in the tropical Martian atmosphere

Evidence for widespread nonuniform vertical mixing of dust in Marss tropical atmosphere (in the form of features called “detached dust layers” or DDLs) is a challenge for atmospheric modeling. We characterize the seasonal, diurnal, and geographic variability of DDL activity in retrievals from observations by the Mars Climate Sounder onboard Mars Reconnaissance Orbiter. We find that dust injection above the boundary layer, which forms DDLs, is a spatially ubiquitous phenomenon in the tropics during the daytime, implying that it has a significant nontopographic component. DDL formation is more intense in northern spring and summer than in southern spring and summer but is still common when the zonal average dust distribution appears uniformly mixed. DDLs do not appear to follow the upwelling associated with Marss Hadley circulation or the extant climatology of local dust storm activity in the tropics. Geographic variability in the nightside vertical dust distribution does not always correlate with the dayside vertical dust distribution, implying that there is spatial and seasonal variability in the efficiency of dust deposition/removal processes. Nighttime dust removal is especially efficient over the Tharsis Montes during northern spring and summer, which suggests some association between water ice clouds and removal. Intense injection combined with efficient removal results in a high amplitude of diurnal variability in the dust distribution at 15–30 km above the surface of the tropics during much of the Martian year.

Extreme detached dust layers near Martian volcanoes: Evidence for dust transport by mesoscale circulations forced by high topography

Modeling suggests that thermal circulations over Marss highest volcanoes transport water vapor and dust from the surface into the middle atmosphere, forming detached layers in these constituents. Intense vertical mixing also takes place in regional and global dust storms, which can generate detached layers that are extreme in both altitude and magnitude. Here we employ observations by the Mars Climate Sounder (MCS) on board Mars Reconnaissance Orbiter, taking advantage of improved vertical coverage in MCSs aerosol retrievals, to discover a new class of extreme detached dust layers (EDDLs). Observed during minimal dust storm activity and furthermore distinguished by their potentially large and measurable horizontal extent (>1000 km), these EDDLs cluster near Olympus Mons and the Tharsis Montes, from which they likely originate. The existence of these EDDLs suggests that vertical mixing by topographic circulations can be much stronger than previously modeled and more frequent than previously observed.

Discovery of a widespread low‐latitude diurnal CO2 frost cycle on Mars

While the detection of CO2 ice has only been reported outside the Martian polar regions at very high elevation (i.e., Elysium, Olympus Mons, and the Tharsis Montes), nighttime surface observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter document the widespread occurrence of atmospherically corrected ground temperatures consistent with the presence of extensive carbon dioxide frost deposits in the dusty low thermal inertia units at middle/low latitudes. Thermal infrared emissivities, interpreted in conjunction with mass balance modeling, suggest micrometer size CO2 ice crystals forming optically thin layers never exceeding a few hundreds of microns in thickness (i.e., 10−2 kg m−2) locally, which is insufficient to generate a measurable diurnal pressure cycle (<<0.1% of the Martian atmosphere). Atmospheric temperatures at middle/low latitudes are not consistent with precipitation of CO2 ice, suggesting that condensation occurs on the surface. The recurring growth and sublimation of CO2 ice on Martian dusty terrains may be an important process preventing soil induration and promoting dynamic phenomena (soil avalanching and fluidization and regolith gardening), maintaining a reservoir of micrometer size dust particles that are mobile and available for lifting. The discovery of this diurnal CO2 cycle represents an important step forward in our understanding of the way the Martian atmosphere interacts with the surface.

Extreme eolian delivery of reactive iron to late Paleozoic icehouse seas

The biogeochemical impacts of iron-rich dust to the oceans are known for Earth’s recent record but unexplored for deep time, despite recognition of large ancient dust fluxes, particularly during the late Paleozoic. We report a unique Fe relationship for Upper Pennsylvanian mudrock of eolian origin that records lowstand (glacial) conditions within a carbonate buildup of western equatorial Pangaea (western United States) well removed from other detrital inputs. Here, reactive Fe unambiguously linked to dust is enriched without a corresponding increase in total Fe. More broadly, data from thick coeval loess deposits of western equatorial Pangaea show the same marked enrichment in reactive Fe. This enrichment—atypical compared to modern marine, fluvial, glacial, loess, and soil sediments—suggests an enhancement of the reactivity of the internal Fe pool that increased the bioavailability of the Fe for marine primary production. Regardless of the mechanism behind this enhancement, our data in combination with other evidence for high dust fluxes imply delivery of extraordinarily large amounts of biogeochemically reactive Fe to glacial-stage late Paleozoic seas, and modeling of this indicates major impacts on carbon cycling and attendant climatic feedbacks.

Abrupt and high-magnitude changes in atmospheric circulation recorded in the Permian Maroon Formation, tropical Pangaea

Geochemical, magnetic, sedimentologic, and U-Pb detrital zircon data from loessitepaleosol couplets within the Maroon Formation of Colorado (western U.S.) record abrupt and high-magnitude changes in atmospheric circulation in western tropical Pangaea during Early Permian (Wolfcampian) time. The relative quartz grain size increases by 50%–100% in loessite compared to superjacent paleo sols. Quartz grain size correlates inversely with bulk magnetic susceptibility (r 2 = 0.89); susceptibility values from paleosols are two times higher than from underlying loessite. This pattern is interpreted to refl ect high-frequency shifts in dust-transporting wind intensity. Loessite represents semi-arid times when dusttransporting winds were stronger, depositing coarser sediment, whereas paleosols record accumulation of fisediment marked by pedogenic enhancement of magnetic susceptibility within a wetter, less windy climate. Both major- and trace-element geochemistry differ between the loessite and superjacent paleosols. The paleosols are more phyllosilicate rich, likely tied to differences in grain size. However, a multivariate analysis of log-transformed trace-element data suggests that the thicker loessite units exhibit a shift in provenance compared to paleosols and thinner loessite units. U-Pb ages of detrital zircons also differ between loessite and paleosols. Four couplets were analyzed; all loessite samples contain at least one grain with U-Pb ages (1) <300 Ma and (2) 760–940 Ma, whereas no paleosol sample contains these ages. The fi rst population refl ects coeval arcs fringing western Pangaea and eastward transport in a westerly wind regime. The second population is more enigmatic but may refl ect erosion of Proterozoic rift-related volcanics, located along the western edge of Pangaea or located in northern Canada. In addition, the loessite samples contain a lower ratio (0.69) of Neoproterozoic grains (760–570 Ma) to Paleozoic grains (500–300 Ma) compared to paleosols (1.32). Both loessite and paleosol samples contain zircons with U-Pb ages between 1360–925 Ma and 1800–1610 Ma. The Neoproterozoic, Paleozoic, and 1360–925 Ma (Mesoproterozoic) grains were sourced from the Appalachian-Ouachita orogen to the east to southeast, whereas the 1800–1610 Ma (Paleo proterozoic) grains refl ect local basement uplifts (Ancestral Rocky Mountains). Overall, the combined geochemical and detrital zircon data indicate changes in provenance tied to abrupt and repeated changes in the direction of dust-transporting winds. The loessite-paleosol pairs exhibit a nested stratigraphy with a thick paleosol capping a thick loessite followed by thinner loessites grading into thinner, and less well-developed, paleosols. Our data suggest that thick loessite intervals accumulated in a monsoonal climate with strong, seasonal westerly winds coupled with semi-arid conditions, whereas the superjacent thick paleosol records more humid climate and a provenance derived primarily from the east. The muted sedimentologic, magnetic, and geochemical differences exhibited in the series of thinner loessitepaleosol couplets likely refl ect muted climate change. In this model, the thick loessitepaleosol couplet represents a period of major glaciation and the subsequent interglacial, respectively, in which a more elliptical Earth orbit accentuates climatic extremes. The thinner couplets likely represent more circular Earth orbits during times of advancing glacial conditions when climatic extremes were muted. The inferred depositional duration of the Maroon Formation indicates these

The reflectivity of Mars at 1064 nm: Derivation from Mars Orbiter Laser Altimeter data and application to climatology and meteorology

The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS) made > 108 measurements of the reflectivity of Mars at 1064 nm (R 1064) by both active sounding and passive radiometry. Past studies of R 1064 neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry. Therefore, as yet, there exists no acceptable reference R 1064 to derive a column opacity product for atmospheric studies and planning future orbital lidar observations. Here, such a reference R 1064 is derived by seeking R 1064 M , N : a Minnaert-corrected normal albedo under clear conditions and assuming minimal phase angle dependence. Over darker surfaces, R 1064 M , N and the absolute level of atmospheric opacity were estimated from active sounding. Over all surfaces, the opacity derived from active sounding was used to exclude passive radiometry measurements made under opaque conditions and estimate R 1064 M , N . These latter estimates then were re-calibrated by comparison with RM,N derived from Hubble Space Telescope (HST) observations over areas of approximately uniform reflectivity. Estimates of R 1064 M , N from re-calibrated passive radiometry typically agree with HST observations within 10 %. The resulting R 1064 M , N is then used to derive and quantify the uncertainties of a column opacity product, which can be applied to meteorological and climatological studies of Mars, particularly to detect and measure mesoscale cloud/aerosol structures.